The present invention relates to the field of pneumatic valves and more particularly to a time delay valve for controlling the discharge of a fluid medium, such as a fire suppressant medium.
With the ever increasing use of fully integrated fire suppressant systems which despense suppressant agents such as CO.sub.2 or Halon over an area under surveillance, a need has arisen for a low cost, easily maintained time delay apparatus for operating the system. The time delay of a short period in the order of 60 seconds is necessary to allow the area to be evacuated by personnel prior to discharge of the suppressant and to allow the discharge operation to be countermanded, if it was unnecessarily activated. This latter point is particularly important where the discharge of suppressant would severly damage equipment, such as electronics and particularly computers.
Time delay mechanisms for use in suppressant systems have been proposed in the past by have not adequately fulfilled the needs of the industry. These delay mechanisms are inadequate for various reasons including depending on external electrical power which may fail during a fire emergency requiring pressure regulation or depending on a complex arrangement of springs and diaphragms which must be continuously checked and maintained to assure proper functioning. See, for example, Williamson et al., U.S. Pat. No. 2,758,657.
Allen et al., U.S. Pat. No. 2,537,009 discloses a time delay valve in which the fluid is first bled into a storage chamber, then into a second actuation storage chamber which, after pressurization moves a valve to release the fluid in the first chamber to unseat the control valve. Fluid flow through the device is controlled by a complex array of spring loaded slide valves.
Schrank, U.S. Pat. No. 2,865,592 discloses a delayed action valve which uses carbon dioxide pressure to operate a piston valve. The gas is fed through a metering tube into a storage container until sufficient pressure builds up to operate the spring loaded dispensing valve. Similarly, Ludwig U.S. Pat. No. 3,256,906 discloses a bi-directional, spring loaded delay valve for air circuits.
Finally, Grant U.S. Pat. No. 2,663,153 discloses a fluid pressure operated spring loaded valve which utilizes an accumulator receptacle that is pressurized until the set pressure for operating the dispensing valve is reached.